Retort furnace for pyrolysis of fuels



United States Patent O 3,108,930 RETGRT FURNACE FR PYRLYSlS F FUELS leRudolf Lennart Brandherg, rebro, Sweden, assigner to Svenska Skiterolie Aktiebolaget, Grebro, Sweden,

a company of Sweden Filed Jan. 27, 1958, Ser. No. 711,502 Claims priority, application Sweden Feb. 6, 1957 2 Claims. (Cl. 292-114) ranged in line longitudinally of the shaft, said retorts opening into a combustion chamber for pyrolysis residues which is disposed in the lower part of the shaft. As a rule the retorts have hitherto been provided with a circular cross section and have been slightly -tapered upwards. The retorts are continuously charged at the top and the distillation gases are usually taken out through tubes which have been brought down to the central or lower section of the retort.

lt has now been found that high yields of oil and gas are obtained if the shale is heated to a certain temperature, as rapidly as possible and maintained at this temperature level at least for a certain time and 'the pyrolysis vapours are quickly conducted away from the hot zone. If the heating takes place too slowly, secondary reactions start affording a less amount of oil. In shale, the oil is formed from the kerogene over a series of intermediate products which are thermally more and more stable and decompose with a slower and slower velocity, and the heating of the shale should lbe carried out to such an elevated temperature that all oil forming reactions take place and are maintained at high temperature for a period of time suliiciently long for the oil formation to be completed and the oil to be vaporized. A still more elevated temperature and an extended timeat-temperature do not increase the oil formation although gas formation continues long after the oil formation has ceased. It is diicult to attain good pyrolysis results in the case of using as a fuel available pyrolysis residues, which at least in shale are poor in calories and are easily sintered. Among other things the quantity of combustion gas lis small and the gas velocity in the shaft low, even if the retorts occupy a great part of the shalft area and the flow is laminar or in the transient zone.

Practical observations and theoretical conside-rations have led to the possibility of the 'above mentioned experiences being put into practical operation of pyrolysis furnaces by, according to the invention, the furnace being built in such a way that the retorts, at least at their bottom sections, have a cross section which is substanltially larger, suitably about 1.5-4, for instance 2-3, times larger transversely of the shaft than longitudinally of the same, rand tha-t the retorts have a total cross section area covering at least 1/3, preferably at least one half suitably about 55-60% of the cross section area of the shaft at the bottom section of the retorts. Then the distance be- 7'j tween the retorts should be adjusted with respect to their 'cross section shape so that the retorts at least at their bottom sections are substantially uniformly and evenly irradiated by the Walls of the shaft.

Furthermore, it has been found that the cross section shape of the retorts has an extremely great importance for the heat transmission inside the retorts, which has a considerably greater influence upon .the pyrolysis process than has been previously appreciated. Therefore in an important embodiment of the invention the shortest distance from every point of the cross section of the retorts to the retort wall is less than l preferably less than l2,

for instance about 8-12 times the mean particle size of CFI ateatro "ice the pyrolysis material. In the oase when shale is crushed to a mean size of about l0 mm. it is thus 'advisable that said shortest distance is less than 150 mm. and preferably about 100 mm., which also has been .confirmed by practical observations, as well as the fact that the shortest distance in material having a mean particle size of about mrn. preferably is about 350 mm. Hence it follows that in order for more ideal conditions t0 be attained the pyrolysis material should be divided into particle fractions and :each fraction be pyrolyzed by itself in retorts properly Idimensioned therefor. As a matter of course dust fractions should ybe completely avoided in retorts having the :above mentioned dimensions.

According to another embodiment of the invention the retorts are designed in such a way that the extension of their cross sections decreases, preferably only transversely of the shaft, so that lthe cross section area is at least about twice, preferably about three times, as large at the bottom as it is at the top. Herreby not only retort material is saved but, in addition, there is realized the advantage that the material comparatively rapidly passes the low temperature zone and gets a relatively long staying time in the high temperature zone, where the pyrolysis pro-per takes place. Besides, ya more or less unavoidable sucking in of air through the charge opening is highly Ireduced.`

For the sake of retort strength and transfer of material in the retort, it is advisable that the cross section of the retort is rounded, at least at the lower half of the retort, and preferably with a concaveness at the centre of one or both long vsides where suitably an inner bracing member is disposed for instance, in the shape of a possibly openwork partition wall..

For heating the lowermost parts of the retorts 'the surface radiation from the bed and shaft wall is dominating. On the other hand there is no, doubt about the fact that for the most part .the total heat supply to the retorts passes over the gas phase. The retort walls are of no importance for the lieat transmission as long as they are made of steel.

The increase in the size of the retorts also enables the traversing speed of the shale to be considerably increased without the pyrolysis result being impaired in comparison with previously used circular retorts. The enlargement of the retort and the increase in traversing speed may be carried on until fthe heat transmission to the outside of the retort begins to strongly affect the heat transmission to the interior of the shale mass so that the whole temperature level in the shaft is lowered. Before this occurs optimum conditions for the pyrolysis have been attained for the retort furnace.

In the attached drawing the invention is shown diagrammatically, as an example of the same being employed in a retort furnace of a type previously known and described. FIGURE l shows a vertical cross section and FIGURE 2 a horizontal cross section of the furnace according to the invention, while FIGURES 3-5 show an embodiment of a retort as viewed in a plane normal to the major cross-sectional axis, in a plane normal to the minor cross-sectional axis, and from the top respectively.

As may be seen from FIG. l, a retort 1 is depending from a cover construction 7 in a shaft 5 lined with ceramic material 3. At the top of the retort is provided in a known manner with a feeding hopper 9 and a central gas tube 11 for sucking away the pyrolysis vapours through the header 13. At the bottom the retort opens out into the combustion chamber 15 which in operation is filled with burning pyrolysis residues. The solid fuel residue is vdischarged by means of the rotatable grate members 17.

The cross section of the retorts lshould be longer than broad but, as shown in FIG. 2, its design in details may vary. Thus the retorts 1a are provided with hat longsides and rounded short-sides; the retort 1b has, in crosssection the general configuration of the numeral 8 the walls being rounded and centrally drawn together. The retorts 1c externally look like the retorts 1b but they are provided internally with a bracing member 19.

As shown in FIG. 2, the retorts are so dimensioned, with respect to the shaft, and are so disposed within the shaft that at their bottom sections the distance between their long sides and the shaft Wall is substantially the same as is the distance between their short sides and the shaft wall, and such distance is substantially the same as is the distance between any two adjacent retorts. In this Way the bottom sections of the retorts are substantially uniformly and evenly irradiated by the walls of the shaft.

As shown in the FIGURES 3-5, the retort may taper upwards in one direction but have the same width in a direction at right angles thereto so that at the top it terminates in the form of a hollow cylinder 21. In FIG. 5 an optional bracing member 19 may be seen.

The retort furnace according to the invention has been the object of comprehensive practical trials. Thus it has shown that in a shaft furnace having a cross section of 0.6 x 1.5 m. and containing 5 retorts according to FIGURES 3-5, 2.75 m. long and having a circular cross section at the top with a diameter of 190 mm. and an elongated cross section at the bottom of 190 X 440 mm. (in which retorts shale material of 5-25 mm. lump size suitably is used) the optimum shale traversing speed for the oil production could be increased more than 30% while simultaneously the oil and gas yield were improved during the pyrolysis in comparison with pyrolysis in the same shaft with previously used, slightly tapering circular retorts having a diameter of 278 mm. at the bottom, other dimensions being the same as those of the just mentioned retorts. By means of retorts of the same length and having cross sectional dimensions of 190 x 255 mm. at the top and 190 x 500 mm. at the bottom, the optimum shale traversing speed could be increased in the same shaft by more than What I claim is:

1. A furnace for pyrolysis of fuel, such as shale, comprising a refractory shaft and a plurality of retorts arranged within a common space in the shaft and in line longitudinally of the shaft, said retorts opening into a combustion chamber for pyrolysis residues which is disposed in the lower part of the shaft, characterized in that the retorts are symmetrically arranged in the common space within said shaft and in mutually radiating relation to each other, and in that said retorts at least at their bottom sections have a horizontal cross-section which is about 1.5-4 times larger, transversely of the shaft than longitudinally of the same, and that the retorts have a total cross section area covering at least one-half of the cross section area of the shaft at the bottom section of the retorts, and further characterized in that heating members external to said retorts are provided in said shafts as sole heating means.

2. A furnace according to claim 1, characterized in that the cross section of the retorts tapers upwardly, so that the horizontal cross section area is at least about twice as large at the bottom as it is at the top.

References Cited in the file of this patent UNITED STATES PATENTS 1,127,228 Glover et al. Feb. 2, 1915 1,176,432 Chrisman Mar. 21, 1916 1,704,093 Marshall Mar. 5, 1929 1,704,103 Rodgers Mar. 5, 1929 2,550,677 Dalin etal May 1, 1951 FOREIGN PATENTS 664,203 Great Britain Oct. 4, 1950 

1. A FURNACE FOR PYROLYSIS OF FUEL, SUCH AS SHALE, COMPRISING A REFRACTORY SHAFT AND A PLURALITY OF RETORTS ARRANGED WITHIN A COMMON SPACE IN THE SHAFT AND IN LINE LONGUTUDINALLY OF THE SHAFT, SAID RETORTS OPENING INTO A COMBUSTION CHAMBER FOR PYROLYSIS RESIDUES WHICH IS DISPOSED IN THE LOWER PART OF THE SHAFT, CHARACTERIZED IN THAT THE RETORTS ARE SYMMETRICALLY ARRANGED IN THE COMMON SPACE WITHIN SAID SHAFT AND IN MUTUALLY RADIATING RELATION TO EACH OTHER, AND IN THAT SAID RETORTS AT LEAST AT THEIR BOTTOM SECTIONS HAVE A HORIZONTAL CROSS-SECTION WHICH IS ABOUT 1.5-4 TIMES LARGER, TRANSVERSELY OF THE SHAFT THAN LONGITUDINALLY OF THE SAME, AND THAT THE RETORTS HAVE A TOTAL CROSS SECTION AREA COVERING AT LEAST ONE-HALF OF THE CROSS SECTION ARE OF THE SHAFT AT THE BOTTOM SECTION OF THE RETORTS, AND FURTHER CHARACTERIZED IN THAT HEATING MEMBERS EXTERNAL TO SAID RETORTS ARE PROVIDED IN SAID SHAFTS AS SOLE HEATING MEANS. 